This invention relates to heat recovery systems for forced air furnaces fueled by combustible fuels such as natural gas, propane, butane and fuel oil.
Most commercial and home forced air furnaces operate at only some 65% to 75% efficiency. This relatively poor efficiency is due in large part to the loss of heat conducted out of the home by the flue gases eminating from the furnace. In an attempt to recover this heat loss heat exchangers have heretofore been mounted within the furnace flues through which exchanges ambient home air is drawn and then channeled to the furnace air return duct to preheat the intake air. Such heat recovery systems are exemplified by those illustrated in U.S. Pat. Nos. 1,586,228, 2,265,501 and 2,738,785. A variation of this type system is disclosed in U.S. Pat. No. 2,362,940 wherein air is routed from the heat exchanger mounted within the furnace flue back to the home rooms themselves rather than to the furnace return air duct.
These early attempts to recover heat losses from escaping flue gases have not met with substantial success. Perhaps the foremost reason for this lack of success is attributable to the relatively small amount of heat transferred to the air passing through the exchangers to the furnace. This in turn has been occasioned in large part by the relatively slow flow of air drawn by the furnace blower back into the heating system through the heat exchanger. In attempts to increase this flow the heat exchangers have been provided with auxiliary blowers as disclosed in U.S. Pat. Nos. 2,468,909, 3,124,197 and 3,813,039. The addition of such auxiliary blowers itself, however, creates an overall decrease in energy economization due to that consumed in operating the blower plus the attendant cost of manufacture, installation and service. Furthermore, the heat exchangers themselves have been of relatively complex and costly design as well as expensive and difficult to incorporate into preinstalled furnace flues.
Accordingly, it is a general object of the present invention to provide an improved heat recovery system for forced air furnaces fueled by combustible fuels such as gas and oil.
More specifically, it is an object of the present invention to provide an improved system for recovering heat losses in flue gasses emanating from forced air furnaces.
Yet another object of the invention is to provide a heat exchanger of improved construction for utilization in a heat recovery system of the type described.
Yet another object of the invention is to provide a heat recovery system of the type described with improved air flow without requiring the use of a blower auxiliary to that employed by the forced air furnace itself.